All hail the “Anti-Mars!”
No less than two astro-events mark the passage of Astronomy Day on October 20th, a day so cool, we repeat it twice! The other Astronomy Day on the calendar for 2012 was on April 28th. (Hey, the sky changes, y’know?)
First up, the planet Mars meets the bright star Antares (a.k.a. Alpha Scorpii), passing just over 3° degrees to its north on the 20th. Mars has added an appreciably different look to the constellation since passing into Scorpius and sliding by Delta Scorpii on October 10th. Coincidentally, now is a good time to compare Mars and its astronomical antithesis. The name “Antares” Means “The Rival of Mars” in Greek (that’s straight outta Burnham’s) a nod to the ruddy star’s Mars-like appearance. The fact that Scorpius hangs on the dusty southern horizon for northern hemisphere observers no doubt adds to this effect. Antares is the only other M-Type supergiant star in the 1st magnitude range (the other being Betelgeuse) and is one of four 1st magnitude stars close enough to the ecliptic to encounter the Moon & classical planets. (The other three being Aldebaran, Regulus and Spica. In fact, we caught the nearly Full Moon in the act of occulting Antares here from Astroguyz HQ back in 2009!
The view on October 20th. (Created by the Author using Starry Night).
Antares shines at an apparent magnitude of +1.1, and has a B-V color index (a good gauge of ‘redness’) of +1.8. For contrast, last week’s featured carbon star TX Piscium had a B-V index of +2.6. Aim a telescope at Antares and crank up the magnification and you just might tease out its +5.5 magnitude companion about 3” arc seconds away.
Mars shines at magnitude +1.4 this week, but that’s where the similarities end. Mars displays a 4.7” arc second disk and is currently just under 17 light minutes distant, while Antares is 550 light years away. Check out the pairing low in the dusk this week… which one looks ‘redder’ to you? Would the “real Ares” please stand up?
The Orionid meteor shower also peaks on the morning of October 20th. This shower typically falls in the 15-30 range in regards to its Zenithal Hourly Rate (ZHR), but recent outbursts in the 2006-2009 seasons saw this shower on the upswing, reaching a ZHR as strong as 70. The source of this shower is no other than that most famous of comets, 1P/Haley. In fact, Halley’s Comet has been identified as the progenitor of two annual showers, the other being the Eta Aquarids in early May. This year is also particularly favorable for the Orionids, as the Moon will be a 5-day old waxing crescent and well out of the morning sky.
And speaking of the Moon, the slender crescent Moon will sit very near the planet Mercury low in the dusk on the evening of October 16th. In fact, the Moon will actually occult -0.2 magnitude Mercury for a very few Earthly residents in and around Nome, Alaska. The Moon is 38 hours old (New phase occurs at 12:02UT on October 15th), and US East Coast residents will have a chance to catch the pair three hours prior at 35 hours past New immediately after sunset on the evening of the 16th, a great astrophotography challenge leading into Astronomy Day!